1. Field of the Invention
The present invention relates to providing a visual warning of the presence of an emergency or highway maintenance vehicle and, particularly, to the generation of plural, multiple intensity, overlapping light flash patterns which afford enhanced visibility in the presence of particulate matter in the ambient atmosphere. More specifically, this invention is directed to a warning light employing two different types of light generator and, especially, to such a warning light wherein the two types of light generator provide pulses having differing lengths and maximum light intensity and are controlled to produce overlapping flash patterns which enhance visibility in the presence of reflective particulate matter in the operating environment. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
2. Description of the Prior Art
While not limited thereto in its utility, the present invention is particularly well suited for use in providing a visual warning of the presence of official vehicles under inclement atmospheric conditions such as snow, rain or fog. Thus, for purposes of illustration, the present invention will be described in association with the potential use thereof on slow moving vehicles employed in snow removal. Such vehicles must, of course, "announce" their presence to other vehicles on the roadway. Safety considerations dictate that such other vehicles be warned of the presence of the snow removal vehicle from as great a distance as possible since, under conditions of snow removal, vehicle stopping distances are exaggerated. At the same time, the means by which the presence of the snow removal vehicle is announced must not "blind" the operator of either that vehicle or any approaching vehicles to hazards such as, for example, stalled vehicles or other traffic which is being overtaken.
The two above briefly-discussed requirements have, in the past, presented a dilemma to the designer of a warning light. Maximum distance visibility requires that the light pulses generated by a warning light be as intense as possible. Maximum light intensity, in turn, dictates the employment of a "strobe" light, i.e., a periodically energized gaseous discharge tube. Strobe lights generate intense, short duration light pulses with a relatively high pulse repetition rate. Such high frequency light pulses, in a clear atmosphere, are readily visible from a safe stopping distance and do not interfere with the ability of the operator of the vehicle on which the strobe light is mounted to see potential obstructions. In the presence of falling snow, however, as a result of the frequency of the generated light pulses and the movement of the vehicle, a stroboscopic effect may occur. That is, the snow particles will appear to stop in space, i.e., there is an inherent tendency for the eyes of an observer to focus on the particles and this tendency, at the very least, presents a distraction. Additionally, the light reflected from the "stopped" or apparently slow moving particles, partly as a consequence of the relatively slow reaction time of the iris of the human eye to changes in light intensity, may "blind" both the operator of the vehicle on which the strobe light is mounted and the operators of any approaching vehicles, i.e., the bright and substantially constant light resulting from reflection can significantly impede the ability of individuals to detect objects. In summary, under ambient conditions such as blowing snow, dense fog or rain, a strobe light may not afford the optimum solution to the problem of safely providing a readily noticeable visual warning of the presence of an emergency vehicle.
As an alternative to the employment of a gaseous discharge tube light source in a warning light, resort may be had to certain types of incandescent lamps which generate relatively intense light. Thus, warning lights for emergency vehicles often employ, for example, periodically energized halogen lamps. The maximum intensity of the light generated by a halogen lamp is, however, less than that which will be generated by a flash tube. As a general rule, accordingly, a halogen lamp, even when the light generated thereby is focused employing a mirror and/or lens, cannot be seen from as great a distance as a strobe light. The flash repetition rate obtainable from an incandescent lamp is much lower than that customarily generated by a strobe light and will typically be at a frequency which will not result in a stroboscopic effect in the operating environment being discussed. In summary, while employment of an incandescent lamp can avoid the possibility of the above-discussed stroboscopic effect, the reduced penetration, resulting from the lower peak intensity of the incandescent lamp when compared to a strobe light, dictates against the use of an incandescent lamp in a warning light intended for use where visibility is drastically reduced by air borne particles.
Enhancement of the noticeability of incandescent lamps by combining such lamps with a high intensity light source such as a flash tube has previously been proposed. In such prior art combinations, for example as exemplified by the traffic signal disclosed in U.S. Pat. No. 3,895,345, the two different light generators cooperate with a common reflector. Accordingly, at least one of the sources must be displaced from the focal point of the reflector and the available light is thus not utilized in the most efficient manner. Typically, the flash tube has been located so as to surround the incandescent lamp and the reflected light emanating from the flash tube is thus not columnated into a focused beam which affords maximum visibility. Combined light sources for use on emergency vehicles have also been proposed as disclosed in U.S. Pat. Nos. 4,480,211 and 4,958,143. The individual light generators of the prior art systems, as disclosed in these patents, have not been subjected to control in a manner which will provide a light output which takes advantage of the attributes of both types of source while reducing or eliminating the disadvantages thereof when operated in the environment of a particulate matter laden ambient atmosphere.